U  S.  DEPARTMENT  OF  AGRICULTURE. 

BUREAU  OF  PLANT  INDUSTRY— BULLETIN  NO.  141,  PART  V. 


B.  T.  GALLOWAY,  Chief  of  nureau. 


THE  PRESENT  STATUS  OF  THE 
CHESTNUT  BARK  DISEASE. 


HAVEN  METCALF,  Pathologist  m  Charge, 

AND 

J.  FRANKLIN  COLLINS,  Special  Agent, 
Investigations  in  Forest  Pathology. 


Issued  August  30,  1909. 


WASHINGTON: 

GOVKHNMENT     PRINTING     OFFICE. 

1909. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Boston  Library  Consortium  IVIember  Libraries 


http://www.archive.org/details/presentstatusofc01metc 


CONTENTS. 


Page. 

History  of  the  chestnut  bark  disease 4.5 

Present  distribution 45 

Cause  and  symptoms 47 

Restriction  of  spread -  49 

How  the  further  spread  of  the  bark  disease  may  be  limited 49 

By  the  inspection  of  diseased  nursery  stock 49 

By  the  prompt  destruction  of  diseased  trees 50 

By  the  treatment  of  diseased  trees 50 

Conclusions 52 

Bibliography 55 


ILLUSTRATIONS. 


PLATE. 

Pas 


Plate  IV.  Fig.  1. — Large  chestnut  trees  killed  by  the  bark  disease.  Fig.  2.  — 
An  orchard  tree  showing  recently  girdled  branches.  Fig.  3. — 
Part  of  a  diseased  branch  of  a  chestnut  tree,  showing  typical 
pustules  and  form  of  spore  discharge  in  damp  weather 48 


TEXT   FIGURE. 


Fig.  2.  Map  of  the  eastern  portion  of  the  United  States,  showing  the  distri- 
bution of  the  chestnut  bark  disease 46 


B.   P.   1.-484. 

THE  PRESENT  STATUS  OF  THE  CHESTNUT 
BARK  DISEASE. 

By  Haven  Metcalf,  Pathologist  in  Charge,  and  J.  Franklin  Collins,  Special 
Agent,  Investigations  in  Forest  Pathologg. 


HISTORY   OF   THE   CHESTNUT   BARK   DISEASE. 

In  1904  Mr.  H.  W.  Merkel,  of  the  New  York  Zoological  Park,  ob- 
served a  disease  which  was  destroying  large  numbers  of  chestnut 
trees  in  the  city  of  New  York.  This  disease  is  what  is  now  known 
as  the  chestnut  bark  disease.  Even  at  that  time  it  is  certain  that  it 
had  spread  over  Nassau  County  and  Greater  New  York,  and  had 
found  lodgment  in  the  adjacent  counties  of  Connecticut  and  New 
Jersey.  No  earlier  observation  than  this  is  recorded,  but  it  is  evident 
that  the  disease,  which  would  of  necessity  have  made  slow  advance 
at  first,  must  have  been  in  this  general  locality  for  a  number  of  years 
in  order  to  have  gained  such  a  foothold  by  1904.  Conspicuous  as  it 
is,  it  is  strange  that  the  fungus  causing  this  disease  was  not  observed 
or  collected  by  an}^  mycologist  until  May,  1905,  when  specimens  were 
received  from  New  Jersey  by  Mrs.  F.  W.  Patterson,  the  Mycologist 
of  the  Bureau  of  Plant  Industry.  In  the  same  year  Dr.  W.  A. 
Murrill  began  his  studies  of  the  disease,  publishing  the  results  in  the 
summer  of  1906.  By  August,  1907,  specimens  received  by  this 
Bureau  showed  that  the  disease  had  reached  at  least  as  far  south  as 
Trenton,  N.  J.,  and  as  far  north  as  Poughkeepsie,  N.  Y.,  and  was 
spread  generally  over  Westchester  and  Nassau  counties,  N.  Y.,  Bergen 
County,  N.  J.,  and  Fairfield  County,  Conn. 

PRESENT   DISTRIBUTION. 

The  present  distribiition  of  the  chestnut  bark  disease  is  shown  on 
the  accompanying  map  (fig.  2).  By  this  it  will  be  seen  that  infec- 
tion is  now  complete  in  the  general  vicinity  of  the  city  of  New  York. 
Outside  of  this  area  the  di.sease  alread}^  occurs  at  scattering  points 
in  a  number  of  States.  In  every  case  its  occurrence  has  been  defi- 
nitely authenticated  by  specimens  which  have  been  examined  micro- 

141— V 

45 


46 


PRESENT    STATUS    OF    CHESTNUT    BAEK   DISEASE, 


scopicall}".  Reports  have  been  received  indicating  tliat  the  disease 
is  found  at  man}^  other  places,  but  not  being  substantiated  by 
specimens  these  localities  have  not  been  shown  on  the  accompanying 
maj3.  It  is  only  fair  to  state,  however,  that  such  reports  have  been 
received  from  points  as  remote  as  Cape  Cod,  AVellesley,  and  Pitts- 
field,  Mass. ;  Rochester  and  Shelter  Island,  N,  Y.,  and  Akron,  Ohio. 

The  bark  disease  is  entirely  different  from  a  disease  which  during 
the  past  twenty  years  has  caused  the  death  of  many  chestnut  trees 
on  the  Atlantic  slope,  particularly  south  of  the  Potomac  River.  The 
latter  disease,  which  is  now  being  studied  by  the  Department  of 

Agriculture,  is  asso- 
ciated with  insects,  is 
much  slower  in  action 
than  the  bark  disease, 
and  produces  a  stag- 
headed  condition  of  the 
tree.  It  can  be  quite 
confidently  stated  that 
the  bark  disease  does 
not  3^et  occur  south  of 
Virginia  and  at  only  a 
few  points  in  that 
State. 

Investigations  are  in 
progress  to  determine 
the  origin  of  the  bark 
disease  in  America  and 
the  details  regarding 
its  spread.  The  theory 
advanced  in  a  previous 
publication  of  this  Bu- 
reau," that  the  Japan- 
ese chestnuts  were  the 
original  source  of 
infection,  has  been  strengthened  by  many  facts.  It  yet  lacks  much 
of  demonstration,  however,  and  is  still  advanced  only  tentatively. 

While  the  disease  has  spread  principally  from  the  vicinity  of 
New  York  there  is  much  to  indicate  that  it  occurred  at  other  points 
at  an  early  date.  Chester's  Cytospora  on  a  Japanese  chestnut, 
noted  at  Newark,  Del.,  in  1902,  may  have  been  the  bark  disease. 
Observations  by  the  junior  writer  indicate  that  this  disease  may 
have  been  present  in  an  orchard  in  Bedford  County,  Va.,  as  early 

"Bureau  of  Plant  Industry,  U.  S.  Department  of  Agriculture,  Bulletin  121, 
Part  YI.     1908. 
141— V 


Fig.  2. — Map  of  the  eastern  portion  of  the  United  States, 
showing  the  distribution  of  the  chestnjt  barlv  dis- 
ease. The  heavily  shaded  part  shows  the  counties 
wherein  infection  is  already  complete.  The  round 
dots  show  other  points  where  the  disease  is  positively 
linown    to    occur. 


PRESENT    STATUS   OF    CHESTNUT    BARK    DISEASE^  47 

as  1903,  and  that  in  Lancaster  County,  Pa.,  it  probably  was  present 
as  early  as  1905.  All  other  points  shown  on  the  map  outside  of  the 
area  of  general  infection  a^^pear  to  have  been  infected  only  within 
one  or  two  years. 

The  bark  disease  appears  practically  to  exterminate  the  trees  in 
any  locality  which  it  infests.  A  survey  of  Forest  Park,  Brooklyn, 
showed  "  that  16,695  chestnut  trees  were  killed  in  the  350  acres  of 
woodland  in  this  park  alone.  Of  this  number  about  9,000  were 
between  8  and  12  inches  in  diameter,  and  the  remaining  7,000  or  more 
were  of  larger  size." 

In  a  recent  publication  Dr.  W.  A.  Murrill  estimates  the  financial 
loss  from  this  disease  "  in  and  about  New  York  City  "  at  "  between 
five  and  ten  million  dollars."  The  aggregate  loss  throughout  the 
whole  area  of  country  affected  must  be  much  greater. 

The  bark  disease  occurs  on  both  chestnut  and  chinquapin,  regard- 
less of  age,  origin,  or  condition.  It  does  not  occur  on  any  other 
tree  so  far  as  known.  All  reports  of  its  occurrence  on  the  chestnut 
oak  {Qiiercus  ^^rinus)  have  proved  to  be  unfounded.  It  is  not  yet 
known  whether  the  goldenleaf  chinquapin  of  the  Pacific  coast  {Cas- 
tanojysis  chrysophyUa)  is  subject  to  this  disease. 

According  to  Sudworth,  the  range  of  the  native  chestnut  is  "  from 
southern  Maine  to  northwestern  Vermont  (Winooski  River),  southern 
Ontario,  and  southern  shores  of  Lake  Ontario  to  southeastern  Mich- 
igan; southward  to  Delaware  and  southeastern  Indiana,  and  on  the 
Allegheny  Mountains  to  central  Kentucky  and  Tennessee,  central 
Alabama,  and  Mississippi."  The  range  of  the  chinquapin  is  "  from 
southern  Pennsylvania  (Adams,  York,  Franklin,  and  Cumberland 
counties)  to  northern  Florida  and  eastern  Texas  (Neches  River)." 
The  bark  disease  may,  therefore,  be  expected  to  occur  at  any  point 
within  these  limits,  as  w^ell  as  in  any  other  localities  where  the  chest- 
nut is  grown  as  an  ornamental  or  orchard  tree. 

CAUSE   AND   SYMPTOMS. 

The  disease  is  caused  by  the  fungus  Dictporthe  farasitica  Murrill 
(also  known  as  Valsonectria  parasitica  (Murrill)  Rehm).  The 
spores  of  this  fungus,  brought  by  some  means  from  a  previously  dis- 
eased tree,  enter  the  bark  through  wounds;  possibly  also  in  other 
ways.  The  leaves  and  green  twigs  are  not  directly  affected.  From 
the  point  of  infection  the  fungus  grows  in  all  directions  through  the 
inner  bark  until  the  growth  meets  on  the  opposite  side  of  the  trunk 
or  limb,  which  in  this  way  is  girdled.  The  wood  is  but  little  affected. 
Limbs  with  smooth  bark  attacked  by  the  fungus  soon  show  dead, 
discolored,  sunken  patches  of  bark  covered  more  or  less  thickly  with 
the  yellow,  orange,  or  reddish-brown  pustules  of  the  fruiting  fungus, 

141— V 


48  PRESENT    STATES    OF    CHESTNUT    BARK    DISEASE, 

In  damp  weather  or  in  damp  situations  the  spores  are  extruded  in 
the  form  of  long  irregular  "  horns,"  or  strings,  at  first  greenish  to 
bright  yellow  in  color,  becoming  darker  with  age.  Plate  IV,  figure  3, 
shows  a  part  of  a  branch  of  a  diseased  chestnut  tree  magnified  3| 
diameters.  In  this  illustration  the  typical  appearance  of  the  pustules 
in  damp  weather  and  the  projection  of  the  spores  of  the  fungus  in 
the  form  of  "  horns,"  or  threads,  are  shown.  These  threads  maj'  be 
especially  conspicuous  near  the  edges  of  diseased  areas.  If  the  spot 
is  on  the  trunk  or  a  large  limb  with  very  thick  bark  there  is  no 
obvious  change  in  the  appearance  of  the  bark  itself,  but  the  pustules 
of  the  fungus  show  in  the  cracks  of  the  bark  and,  on  account  of  the 
destruction  of  the  layers  beneath,  the  bark  often  sounds  hollow  when 
tapped.  A  patch  usually  grows  fast  enough  to  girdle  the  branch  or 
trunk  that  it  is  on  during  the  firsl.  summer. 

The  damage  may  not  be  immediately  apparent,  since  the  water 
supply  from  the  roots  continues  to  pass  up  through  the  compara- 
tively uninjured  wood  to  the  leaves,  but  when  in  the  following  spring 
the  new  leaves  are  put  out  they  are  usually  stunted  and  soon  wither. 
The  appearance  of  such  trees  is  very  characteristic.  Plate  IV,  figure 
],  shows  large  chestnut  trees  killed  by  the  bark  disease.  In  this  illus- 
tration the  trees  to  the  left  show  the  characteristic  stunted  foliage, 
which  indicates  that  the}^  were  girdled  during  the  previous  year, 
while  the  tree  on  the  right  having  no  foliage  was  presumabl}^  girdled 
by  the  fungus  at  least  two  summers  before  the  photograph  rej)roduced 
was  taken.  Plate  IV,  figure  2,  shows  an  orchard  tree  with  recently 
girdled  branches.  Nothing  else  except  an  actual  mechanical  injury — 
breaking  off  of  trunk  or  limb — produces  such  an  effect  as  is  shown  in 
these  illustrations.  The  imperfectly  developed  leaves  often  persist  on 
the  dead  branches  throughout  the  summer. 

The  great  damage  Avhich  the  disease  has  done  thus  becomes  most 
apparent  in  the  last  week  of  May  or  the  first  week  in  June,  giving 
rise  to  the  false  but  common  idea  that  the  fungus  does  its  work  at 
this  time  of  the  year,  when  in  reality  the  harm  is  done  during  the 
previous  summer.  If  the  first  attack  is  on  the  trunk,  of  course  the 
entire  tree  dies.  If,  on  the  other  hand,  the  small  branches  are  first 
involved,  the  tree  may  live  for  several  years. 

It  is  very  easy  for  a  person  not  familiar  with  fungi  to  confuse  this 
parasite  with  various  other  fungi  which  occur  commonl}^  on  the  dead 
wood  of  chestnuts  and  other  trees,  such  as  species  belonging  to  the 
genera  Calocera,  Cytospora,  and  Cytosporina.  The  superficial  re- 
semblance is  sometimes  very  strong,  but  a  microscopical  examination 
instantly  reveals  the  true  nature  of  the  organism  in  question.  On 
account  of  this  common  confusion  no  dependable  diagnosis  of  the 
bark  disease  can  be  made  in  a  new  locality  Avithout  a  microscopical 
examination  of  specimens  by  an  expert. 

141— V 


Bui.  141 ,  Pt.  V,  Bureau  of  Plant  Industry,  U.  5.  Dept.  of  Agriculture. 


Plate  IV. 


Fig.  1.— Large  Chestnut  Trees  Killed  by  the  Bark  Disease. 


Fig.  2.— An  Orchard  Tree,  Showing  Recently  Girdled  Branches. 


^* 


.#1^^    ♦^^V^ 


Fig.  3.— Part  of  a  Diseased  Branch  of  a  Chestnut  Tree,  Showing 
Typical  Pustules  and  Form  of  Spore  Discharge  in  Damp  Weather. 


(Magnified  3  diameters.) 


PRESENT    STATUS    OF    CHESTXUT    BARK    DISEASE.  49 

RESTRICTION   OF   SPREAD. 

HOW  THE  FURTHER  SPREAD  OF  THE  BARK  DISEASE  MAY  BE  LIMITED. 

By  the  Inspection  of  Diseased  Nursery  Stock. 

It  becomes  more  and  more  evident  as  this  disease  is  studied  that 
diseased  nursery  stock  is  the  most  important  factor  in  its  spread  to 
distant  points.  In  that  part  of  the  country  where  it  is  already  well 
established  in  the  native  chestnuts  its  progress  is  rapid  and  sure, 
but  there  is  no  evidence  at  present  that  it  is  able  to  pass  to  remote 
districts,  tens  or  hundreds  of  miles  away,  except  on  diseased  nursery 
stock.  Of  course  it  is  conceivable  that  the  spores  are  carried  b}' 
birds.  Such  distribution  would,  however,  follow  in  general  the  great 
lines  of  bird  migration  north  and  south  and  hence  would  not  be  an 
important  factor  in  the  western  spread,  except  locally.  During  the 
summer  of  1908  nearly  everj^  chestnut  nursery  and  orchard  of  impor- 
tance in  the  Atlantic  States  north  of  North  Carolina  was  visited, 
and  very  few  were  found  free  from  the  bark  disease.  Several 
cases  were  observed  where  the  disease  had  obviously  spread  from 
the  nursery  to  adjacent  wild  trees.  This  is  the  only  way  in  which 
the  disease  is  likely  to  spread  beyond  the  Alleghenies. 

It  is  therefore  obvious  that  every  State  in  which  the  chestnut  or 
chinquapin  grows  should  as  speedily  as  possible  pass  a  law  putting 
the  chestnut  bark  "disease  on  the  same  footing  as  other  pernicious 
diseases  and  insect  pests,  such  as  the  San  Jose  scale,  against  which 
quarantine  measures  are  taken.  The  Department  of  Agriculture 
will  be  glad  to  give  detailed  suggestions  or  advice  regarding  the 
framing  of  such  laws.  Inspectors  who  already  have  legal  power  to 
quarantine  against  this  disease  should  now  take  special  care  that 
no  shipment  of  chestnut  stock  escapes  their  rigid  inspection. 

A  campaign  of  education  should  also  be  undertaken  by  patholo- 
gists and  inspectors  in  every  State  in  order  to  acquaint  the  public 
Avith  the  nature  and  appearance  of  the  bark  disease,  so  that  it  may 
be  quickly  recognized  and  stamped  out  in  any  particular  locality  in 
which  it  appears.  The  Department  of  Agriculture  will  cooperate  in 
the  following  ways :  Specimens  from  suspected  trees  sent  in  b}^  any 
l^erson  will  be  promptly  examined  and  the  presence  or  absence  of 
the  disease  reported.  Typical  specimens  showing  the  disease  (with 
the  fungus  previouslj^  killed  by  soaking  in  formalin  to  insure  against 
any  infection  from  this  source)  will  be  sent  upon  application  to 
any  inspector,  forester,  pathologist,  or  other  State  or  experiment  sta- 
tion officer,  to  any  nurseiyman  or  orchardist  growing  chestnuts, 
or  to  any  botanist  or  teacher  of  botany.  So  far  as  the  supply  per- 
mits lantern  slides  and  photographs  will,  upon  application,  be  loaned 
for  special  lectures,  exhibits,  etc.,  to  the  officers  of  States,  experiment 

141— V 


50  PRESENT   STATUS   OF   CHESTNUT   BARK   DISEASE. 

stations,  or  colleges.  B3'  these  means  the  inspectors  first,  and  then 
the  general  pnblic,  may  become  familiar  with  the  appearance  and 
work  of  the  disease  in  localities  that  it  has  not  yet  reached,  and  when 
it  does  appear  may  be  able  to  recognize  it  before  it  is  too  late  to  take 
efficient  measures  against  it. 

Although  its  present  distribution  is  that  shown  by  the  map  (fig.  1), 
the  bark  disease  may  be  confidentl}^  looked  for  in  any  orchard  or 
nursery  in  the  United  States  that  contains  chestnut  trees.  All  such 
places  should  therefore  be  rigidly  inspected  at  the  earliest  possible 
date. 

By  the  Prompt  Destruction  of  Diseased  Trees. 

When  the  bark  disease  is  first  noticed  in  any  localit}^,  all  the 
affected  trees  should  be  immediately  cut  down,  unless,  as  in  the  case 
of  orchard  and  some  few  ornamental  trees,  they  are  of  sufficient  in- 
dividual value  to  warrant  special  treatment.  Diseased  trees  if  un- 
treated are  doomed  to  death  in  any  case.  If  permitted  to  stand, 
every  such  tree  becomes  a  center  of  infection,  certain  to  spread  the 
disease  to  all  neighboring  trees,  and  so  Jong  as  it  will  soon  die  if  left 
to  itself  the  sooner  it  is  cut  down  the  better. 

When  cut,  the  brush  should  be  immediately  gathered  and  burned 
in  order  to  destroy  the  fungus  in  the  bark.  Whenever  the  bark  is 
removed  from  the  trunk,  as,  for  example,  when  the  trees  are  to  be  used 
for  poles,  it  should  be  immediately  burned  with  the  brush.  Even 
when  the  tree  is  to  be  used  for  firewood  an  effort  should  be  made  to 
cut  off  at  least  all  the  diseased  patches  of  bark  on  the  trunk  and 
large  limbs  when  the  tree  is  cut  and  to  burn  this  bark  along  with  the 
brush ;  otherwise  the  brush  and  the  piled  wood  will  continue  to 
spread  infection,  since  it  has  been  found  that  the  fungus  continues 
alive  on  dead  bark  for  at  least  six  months  after  cutting. 

Sprouts  arising  from  the  stumps  of  cut  trees  will  be  free  from  the 
disease  for  the  first  year  at  least,  but  must  then  be  carefully  inspected 
to  be  sure  that  no  infection  has  persisted. 

By  the  Treatment  of  Diseased  Trees. 

During  the  past  two  years  the  Office  of  Investigations  in  Forest 
Pathology  has  been  conducting  certain  experiments  and  collecting 
information  in  regard  to  the  best  methods  of  treating  diseased  trees. 

At  present  it  is  impossible  definitely  to  record  general  beneficial 
results  from  any  of  the  sprayings  which  have  been  undertaken  or  have 
been  under  observation.  .This  may  in  part  be  due  to  the  fact  that  it  is 
yet  too  early  to  judge  satisfactorily  all  the  results  and  in  part,  per- 
haps, to  the  infrequency  of  sprayings. 

141— V 


PRESENT    STATUS    OF    CHESTNUT    BARK    DISEASE.  51 

Observations  and  experiments  seem  to  bear  out  the  statement  that 
it  is  very  improbable  that  any  method  of  sprajnng  can  interfere  with 
the  growth  of  the  fungus  if  it  has  once  established  itself  iii  the  inner 
bark,  but  it  may  be  of  considerable  importance  in  preventing  the 
development  of  spores  which  come  from  other  trees  or  from  other 
parts  of  the  same  tree. 

It  has  already  been  demonstrated  that  the  crotches  of  branches 
and  enlarged  bar?s  of  sprouts  are  very  susceptible  to  infection  because 
they  are  favorable  places  for  the  lodgment  of  water,  dust,  spores,  etc. 
In  a  large  majority  of  cases  infections  are  definitely  known  to  have 
originated  at  a  point  where  the  outer  bark  had  been  injured  in  some 
way,  leaving  the  inner  living  bark  exposed,  or  where  the  entire  bark 
over  a  more  or  less  limited  area  had  been  stripped  from  the  tree  or 
cracked  and  split  away  from  the  wood.  Certain  injuries  which  are 
known  to  have  afforded  entrance  for  the  disease  have  been  of  such  a 
nature  that  thej^  might  easily  be  overlooked,  while  others  have  been 
quite  obvious,  even  to  the  careless  observer.  Among  the  latter  may 
be  mentioned  broken  limbs,  split  limbs,  branches  which  have  been 
carefully  cut  but  not  properly  treated  with  tar  or  paint,  bruises  from 
hames,  plows,  and  cultivators;  also  poor  grafts  and  diseased  grafting 
scions.  Among  the  former  may  be  included  bruises  from  boot  heels, 
climbing  spurs,  holes  made  by  borers  and  other  insects,  knife  and  saw 
cuts,  and  frost  cracks. 

Almost  the  only  treatment  that  can  at  present  be  safely  recom- 
mended as  surely  retarding  the  spread  of  the  disease  to  a  greater  or 
less  extent  is  one  which  will  never  be  of  practical  use  except  in  the  case 
of  orchard  trees  or  certain  valuable  ornamental  trees.  It  consists 
essentialh^  in  cutting  out  the  infected  branches  or  areas  of  bark  and 
carefully  protecting  the  cut  surfaces  from  outside  infection  by  means 
of  a  coat  of  paint  or  tar.  This  cutting  must  be  thoroughly  done  and 
the  bark  of  every  infected  place  entirely  removed  for  a  distance  of  at 
least  an  inch  (where  the  size  of  the  branch  permits)  bej^ond  the 
characteristic,  often  fan-shaped,  discolored  areas  produced  by  the 
growing  fungus  in  the  inner  bark.  All  small  infected  twigs  or 
branches  should  be  cut  from  the  tree,  the  cut  being  made  well  back 
of  the  diseased  area.  A  pruning  knife  with  an  incurved  tip,  a  hollow 
gouge,  or  any  other  clean-cutting  instrument  will  serve  for  cutting 
out  diseased  spots.  So  far  as  the  exigencies  of  the  case  will  permit, 
all  borers'  holes  should  be  cut  out.  It  has  been  repeatedly  observed 
in  the  field  that  infection  often  starts  wdiere  borers  are  at  work,  or 
even  at  the  old  holes  made  by  them.  The  paint  or  tar  may  be  applied 
by  means  of  a  good-sized  brush,  care  being  taken  to  cover  every  part 
of  the  cutting.  Treatment  should  begin,  or  observations  at  least,  at 
the  base  of  the  tree  and  the  fact  ascertained  whether  the  disease  has 

141— V 


62  PEESENT    STATUS    OF    CHESTNUT    BAKK   DISEASE, 

already  girdled  the  trunk.  If  such  is  the  case  it  will  be  a  waste  of 
time  to  attempt  any  treatment ;  instead,  cut  the  tree  down  at  once.  A 
rigid  watch  must  be  kept,  especially  during  the  growing  season,  for 
new  infections  or  infections  which  were  overlooked  in  the  earlier  ex- 
aminations, and  if  any  are  observed  they  must  be  treated  promptly,  as 
above  mentioned.  Constant  vigilance  is  necessary  to  keep  the  disease 
in  check.  It  is  suggested  that  examinations  be  made  about  June  1, 
July  15,  and  September  1.  During  a  very  rainy  or  foggy  season, 
when  conditions  are  particularly  favorable  for  the  growth  of  fungi, 
it  may  be  advisable  to  inspect  as  often  as  once  a  month. 

In  regions  in  which  the  disease  is  so  widespread  that  almost  every 
tree  is  infected,  as,  for  instance,  within  25  miles  of  the  city  of  New 
York,  it  is  extremely  doubtful  whether  any  individual  treatment  will 
pay.  Under  such  conditions  immediate  reinfection  is  almost  sure  to 
occur  at  one  or  more  of  the  small  unnoticed  abrasions  or  injuries 
which  are  quite  certain  to  exist  on  most  trees.  In  a  region,  however, 
where  onh"  isolated  cases  have  yet  appeared  it  is  quite  possible  to 
stamp  out  the  disease,  or  at  least  to  prevent  its  rapid  spread,  by 
promptly  cutting  out  and  carefully  burning  all  diseased  bark  and 
limbs,  thus  destroying  these  new  sources  of  infection.  If  a  tree  is 
too  badly  infected  to  be  worth  treating  it  should  not  be  left  standing, 
for  it  will  then  become  a  continual  menace  to  all  surrounding  chest- 
nuts. 

The  Office  of  Investigations  in  Forest  Pathology  asks  the  cooper- 
ation of  all  persons  who  have  observed  the  disease  or  experimented 
with  it  in  any  way.  If  such  people  will  send  in  an  early  report  of  the 
kind  of  treatment  used,  time  of  treatment,  methods  employed,  and 
results  obtained  (even  if  adverse),  it  may  be  possible  to  arrive  at  an 
earlier  and  more  definite  conclusion  in  regard  to  the  possibilities  or 
impossibilities  of  control  than  would  otherwise  be  the  case. 

CONCLUSIONS. 

It  is  to  be  hoped  that  in  the  economy  of  nature  some  limiting  fac- 
tor will  arise  to  check  the  spread  of  the  bark  disease  before  it  has 
wrought  the  same  destruction  throughout  the  country  that  it  already 
has  in  the  vicinity  of  New  York.  But  at  present  there  is  nothing  in 
sight  that  promises  even  remotely  to  check  its  spread  into  new  ter- 
ritory except  the  general  adoption  of  the  measures  advocated  in  these 
pages.  It  can  not  be  argued  that  because  of  its  apparently  recent 
origin  and  rapid  spread  it  will  soon  disappear  of  itself.  Such  dis- 
eases as  pear-blight  and  peach  yellows  have  been  in  the  country  for 
more  than  a  century  and  yet  show  no  sign  of  abating  except  when 
actively  combated  by  modern  quarantine  methods.  Nor  can  any 
conclusions  be  drawn  from  the  fact  that  chestnuts  in  the  Southern 

141 — V 


PEESENT    STATUS   OF    CHESTNUT   BARK   DISEASE.  53 

States  have  suffered  from  a  disease  during  the  past  twenty  years, 
since,  as  already  stated,  that  is  a  totally  different  thing  from  the 
bark  disease. 

Where  the  bark  disease  is  already  firmly  established  and  has  at- 
tacked 50  per  cent  or  more  of  the  chestnut  trees,  as  in  the  vicinity  of 
the  city  of  New  York,  it  is  probably  too  late  to  try  to  do  anything, 
but  where  the  disease  is  just  appearing  there  is  no  reason  to  doubt 
that  strict  quarantine  methods  will  apply  as  well  to  this  as  to  any 
other  disease,  whether  of  plants  or  animals.  The  question  to  settle  is 
simply  Avhich  is  more  costly— to  use  the  methods  recommended  or  to 
lose  the  trees.     The  people  concerned  must  decide. 

141— V 


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141 — V 
54 

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